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Preparation and corrosion resistance of hybrid coatings formed by PEN/C plus PEO on AZ91D magnesium alloys
Surface & Coatings Technology ( IF 5.4 ) Pub Date : 2020-03-20 , DOI: 10.1016/j.surfcoat.2020.125661
Le Sun , Ying Ma , Jinsong Wang , Lingyun An , Sheng Wang , Zhanying Wang

A novel surface modification technique is developed to further improve the corrosion resistance of AZ91D magnesium alloys. Hybrid coatings were fabricated successfully by a combination of plasma electrolytic nitrocarburizing (PEN/C) and plasma electrolytic oxidation (PEO) on magnesium alloys. The microstructures, element distribution and phase compositions of the coatings were analyzed by SEM, EPMA and XRD, respectively. The potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS) were employed to evaluate the corrosion resistance of the coatings. The results show that PEN/C process predominantly depends on the adsorption and diffusion effects of the active atoms of [N] and [C], and it creates a good substrate surface with predesigned chemical composition to get newly born phases, such as SiC and Si3N4 with excellent properties, in the following hybrid coatings. PEN/C pretreatment also provide a favorable microstructure to enlarge the coating thickness and to make the coating more compact for the hybrid coatings followed. There exists an overlapping phenomenon regarding coating thickness rather than piling up layer by layer during the formation of the hybrid coatings. The hybrid coatings exhibit more excellent corrosion resistance than both single PEN/C modified layers and single PEO coatings. Particularly, the hybrid coatings can provide relatively superior long-term corrosion protection and suppress the occurrence of the localized corrosion for AZ91D substrates. It is worth noting that the key of this investigation is keeping the PEO process unchanged for both PEO treatment only and PEN/C + PEO combining procedure.



中文翻译:

AZ91D镁合金上PEN / C + PEO混合涂层的制备及耐蚀性

开发了一种新颖的表面改性技术,以进一步提高AZ91D镁合金的耐腐蚀性。通过在镁合金上结合等离子电解碳氮共渗(PEN / C)和等离子电解氧化(PEO)成功制造了混合涂层。分别用SEM,EPMA和XRD分析了涂层的微观结构,元素分布和相组成。用电位动力学极化试验和电化学阻抗谱(EIS)评估涂层的耐腐蚀性。结果表明,PEN / C工艺主要取决于[N]和[C]活性原子的吸附和扩散作用,它可以通过预先设计的化学成分形成良好的基材表面,从而获得新生相,例如SiC和C。硅3 N 4在以下混合涂料中具有优异的性能。PEN / C预处理还提供了良好的微观结构,可以扩大涂层厚度并为随后的混合涂层提供更紧凑的涂层。在混合涂层的形成过程中,存在涂层厚度重叠而不是层层堆积的重叠现象。杂化涂层比单一的PEN / C改性层和单一的PEO涂层都具有更优异的耐腐蚀性。特别地,杂化涂层可以提供相对优良的长期腐蚀防护,并抑制AZ91D基材发生局部腐蚀。值得注意的是,这项研究的关键是仅对PEO处理和PEN / C + PEO合并程序而言,保持PEO过程不变。

更新日期:2020-03-20
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